Owing to progress in digital information communication networks and others such as the Internet in recent years, users can now easily access network information through individual-oriented terminals using cellular phones or the like.
In such a digital information communication network, information is transmitted by digital signals. Even when an individual user copies music or video data transmitted via the aforementioned information communication network, it is now possible to obtain copied data without substantially degrading audio and/or image qualities.
Therefore, the right of the copyright owner may be significantly infringed unless appropriate measures are taken for copyright protection when a copyrighted content such as music data or image data is transmitted over the digital information communication network.
However, if copyright protection is given top priority, it may become impossible to distribute content data over the fast-growing digital information communication network. This impairs an interest of the copyright owner, who can essentially collect predetermined copyright royalties for copies of the copyrighted data.
In the above case, it is necessary to inhibit unauthorized further copying of the content data such as copyrighted music data or image data, which was once transmitted to the public over the digital information communication network.
Such a data distribution system has been proposed that a distribution server holding the encrypted content data distributes the encrypted content data to memory cards attached to terminal devices such as cellular phones via the terminal devices. In this data distribution system, a public encryption key of the memory card, which has been verified by a verification authority, and its certificate are transmitted to the distribution server when requesting the distribution of the encrypted content data. After the distribution server confirms the reception of the verified certificate, the encrypted content data and a license for decrypting the encrypted content data are transmitted to the memory card. The license includes a decryption key (which will be referred to as a “content Key” hereinafter) for decrypting the encrypted content data, a license ID for identifying the license, control information for restricting use of the license and others. When distributing the license to the memory card, the distribution server and the memory card generate produce keys, respectively, and the keys are exchanged between the distribution server and the memory card so that an encryption communication path is formed, and the distribution server transmits the license to the memory card via the encryption communication path thus formed. In this operation, the memory card stores the received encrypted content data and the license in an internal memory.
When the encrypted content data stored in the memory card is to be reproduced, the memory card is attached to the cellular phone. In addition to an ordinary speech communication function of the telephone, the cellular phone has a dedicated circuit, which reads out the encrypted content data and the content key from the memory card, decrypts the encrypted content data and reproduces it for external output. For reading the license Key, an encryption communication path is formed between the memory card and the dedicated circuit, and the license Key is transmitted from the memory card to the dedicated circuit via the encryption communication path.
The memory card has a function of shifting or copying the license with respect to another memory card. In this case, the license is transmitted similarly to the case of transmission of the license from the distribution server so that the encryption communication path is formed by functions of both the memory cards on the transmission side and the reception side, and the license is transmitted from the memory card on the transmission side to the memory card on the reception side. The license contains the control information determining whether the license is to be shifted or copied.
The memory card further has a function of performing the following operation. When the license is lost due to accidental interruption of the transmitting or receiving operation, this operation can be resumed, and the last history information relating to input/output of the license is recorded for preventing double transmission of the license, and can be output when necessary. The distribution server or the memory card on the transmission side obtains the history information from the memory card on the reception side, and determines the resuming of the transmission/reception of the license according to this history information. The history information includes the license ID and the status information indicating the transmission and reception.
As described above, the user of the cellular phone receives the encrypted content data and license from the distribution server over the cellular phone network, and stores them in the memory card. Then, the user can reproduce the encrypted content data stored in the memory card, or can shift it to another memory card. Also, the right of the copyright owner can be protected.
However, the conventional memory card holds only the last history information, and the history information relating to the last interruption will be lost when transmission or reception of another license is performed after the interruption. In connection with this, the plurality of items of history information may be stored for improving convenience of the user.
As speeds of access to storage elements and capacities of storage elements have been increasing, it can be presumed that a request for parallel execution of transmission/reception of multiple licenses will occur. For such case, it is necessary to store history information relating at least to the processing performed in parallel.
If the memory card is configured to store the plurality of items of history information for the above purpose, a license received by the memory card may be shifted to another memory card. This causes a problem that history information having different statuses are stored corresponding to the same license ID.